This invention relates to dies for shearing in stamping, and more particularly, to compound die assemblies for performing blanking and piercing at a same press stroke.
Generally speaking, shearing in use of a compound die assembly is employed for high production of small-sized precision parts of metal such as steel, aluminum and others, paper or other materials, because it can readily produce a large number of parts with high dimensional accuracy without dimensional distribution. However, in order to insure the high dimensional accuracy of parts produced, it is required to make dies at high dimensional accuracy. Therefore, cost of the die is quite high so that the stamping in use of the compound die assembly is unsuitable for low production of parts of various shapes.
If the compound die assembly is used for making large-sized parts, weights and size of the die are necessarily increased and therefore, cost is also increased. Furthermore, the die assembly is suffered from difficulty and danger in installation on a press. In particular, it is accompanied with danger to fix a punch unit to the press ram, and there is required skill in die-height adjustment.
On the other hand, a die holder of the compound die assembly is provided with slug clearance holes in order to remove punched slugs, and the compound die assembly is mounted on the press so that the slug clearance holes are disposed over openings of a bolster and a bed of the press. However, in shearing a large-sized blank having holes distributed, there is a disadvantage that punched slugs corresponding to holes at peripheral portion of the blank do not drop into the bolster opening so that the slugs cannot be removed. In order to resolve such a disadvantage, it is thought to use parallel blocks beneath the die holder to form a space between the die holder and the press bolster in which punched slugs are accumulated. However, the central portion of the die holder is maintained unsupported. Therefore, there is a disadvantage that the die holder is bent by pressing force in blanking. Such a disadvantage is increased in blanking parts having many holes concentrated or crowded, complicated holes and/or lengthy slits. In order to resolve such a disadvantage, thickness of the die element and the die holder must be increased, but it results to increase of thickness and weight of the die assembly. Accordingly, the compound die assembly has been thought to be unsuitable for production of large-sized blanks.